The fourth planet in the Sirius system is the only body in the system capable of sustaining life. The planet's single moon is marginally hospitable for life. Sirius IV rotates in 37.5 standard hours and revolves in 389 standard days. Average mean temperature is 84 degrees Fahrenheit and seasonal variation is minimal.

The tropical biosphere of Sirius IV is currently severely compromised as a result of heavy industrialization, overuse of natural resources, and the effects of prolonged war. The only significant bodies of water are located inland as landlocked oceans. On the shores of these oceans are the major centers of population, trade, and commerce. Bordering the oceans are vast jungles that mark the origins of the Sirian people. The planet topography is unremarkable and fairly uniform, excepting a few low mountain ranges and the polar regions.

Since the emergence of reptile life as the dominant species, all mammal life has been virtually exterminated from the planet. Some species, such as the Slon (similar to a Terrestrial pig) and the Grook (a rodent) have been bred for food, but the bulk of Sirian sustenance comes from synthetically-augmented vegetable matter. The Qomp (similar to a Terrestrial ape, but marsupial) has been trained for centuries to perform menial labor for the Sirians.

Capitol city Murkat, home to the Supreme Leader, is located on the shore of the largest inland ocean, Kaal-a-Mat ("Blanket of Life"). The average Sirian citizen has never visited Murkat nor even seen the Leader. Access to Murkat is restricted due to assassination attempts and other security risks. Alliance groups are known to operate from bases deep within the jungles. The far side of Sirius IV was once the site of all military operations, but has since been rendered uninhabitable due to an anti-matter explosion. All operations and military expeditions are now launched from Sirius IV's small moon, and all incoming craft must first dock there.